Insulating Old Concrete Foundation

The owner of the house before me built a little room in the basement to be used as pot growing room. No joke. I ripped it out so I can build a little wine room down there to store wine.

When I ripped out the original drywall and everything there was regular insulation placed right against the old concrete foundation. There was mold all over it and the wood placed against the foundation was basically rotted. I ripped out everything. The frame, the insulation and the drywall. Now I need to start to rebuild the room.

The foundation in this section of the house are the big stone foundation from back in the day. It isn't really flat to place any Styrofoam. I want to use the Styrofoam type of insulation board and put it right against the old concrete. It isn't level so are there any ideas how to fill in the back or can i kind of float the insulation against the wall? Then the frame I put in from of it make sure it is level?

My place is the following:
1) Wire brush the old foundation
2) Fill in areas with the hydraulic sealant
3) Drylok the old foundation where I will be rebuilding the room
4) Float the Styrofoam against the concrete wall
5) Build frame against the insulation
6) Wrap interior of frame with plastic vapor barrier
7) Drywall room.

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Insulating Old Concrete Foundation

BJR,

I actually just replied to a similar query (search "basements" for a recent post), but I also have a few specific comments on your process.

1) I am personally not a big fan of efforts to seal or patch basement foundation walls. There is no harm in it, but, if there is significant water coming in it has to be managed, i.e. channeled or diverted to a drain system. Patching alone is almost a short term fix and not really a good idea if you are going to cover the patched walls. Otherwise that water is still going to find the next easiest way in to your basement. I can almost guarantee that.

2) The experts would steer you to XPS rigid foam over styrofoam. It handles water much better, is still reasonably priced, and is widely available. The box stores have good prices on thinner sheets. Try a concrete/masonry trade supplier for thicker sheets.

3) If you are framing the walls, why spend time prettying/skim coating the foundation walls?

4) Consider metal framing and fiberglass faced wall board.

5) Do not put a vapor barrier on the interior of the wall assembly if you are installing a vapor barrier (the XPS) on the exterior of the wall assembly.

Insulating Old Concrete Foundation

I wasn't going to skim coat the walls. Im just not sure how to use the insulation if it doesn't lay flat on the walls. Can I just attach the insulation to the back of the frame and set it a couple of inches off the wall? I don't really care about the water entering the basement as we have a sumpump and I can somehow funnel the water to it if I have to.

Insulating Old Concrete Foundation

That's the right stuff, extruded polystyrene foam or XPS insulation.

You can use the framing to snug the XPS in place. You don't want it moving around because you want the T&G to stay tight to each other, but there is no other reason to ensure that it sticks to the concrete wall.

Still, you can tack the XPS to wall using adhesives (the box stores sell special ones that won't melt the foam) or with screws or nails and possibly furring strips, and you can use enough of either to hold it in place permanently or just a little to keep it in place while you frame.

Also, you don't need that gap between the framing and the wall if you are using the XPS.

Insulating Old Concrete Foundation

Even though XPS is a vapor retarder, not a vapor barrier, I would use it alone with out an additional poly sheet vapor barrier. Basically, some slow moisture transmission is actually a good thing as it keeps water from getting trapped in the wall assembly. (I didn't dream this up. A little research at the Fine Home Building, Building Science Corporation and Building America web sites should confirm it.)

Still, this is all for vapor, not actual water. The XPS would divert water down to the plates where it will come into the room, but, if you have liquid coming out of your walls, you really need to make sure finishing the basement is a good idea. I have had several clients assure me that they have never had so much water before when they are standing in their brand spanking new finished basement (they did not want to do drain or waterproofing work before the finishing work). I can't help but think that we pay attention a little more closely after sinking $25k into a space than when it was the old rough storage space.

If this is your case, at a minimum, I suggest using metal framing, shimming the floor plate so it sits about a 1/4" above the concrete to allow water through, using a fiberglass faced wall board, and no MDF trim.

Insulating Old Concrete Foundation

Im not going to finish the whole basement. This is probably just 1/6th of the basement. Everything else Im going to leave open. I kind of like to have an unfinished basement because I don't need the living space and it allows me to have a nice work room.

Im not even sure if water is really getting through or not, or if it was just condensation and no room for the water to evaporate. There was no air behind the old room because he put the fiberglass right against the old concrete.

Are there such things as metal shims? Im thinking we should probably shim essentially the whole room 1/4 inch so there is air flow below it. This should help dry up the air as I have a nice big dehumidifier in that room.

So my plan was to only really plug and drylok just the 2 walls where the room will be sitting. There is a sum pump as well in the basement so this helps with the drainage.

Insulating Old Concrete Foundation

Hey bjr149,

If you're only insulating the wine room to control the temperature inside, you may want to just build the wall backwards and not have it directly touch the exterior foundation wall.

What I mean by backwards is to frame the wall that will go against the foundation wall first. Just leave it 1/2 inch short so you can move it. Insulate it with the XPS from the back side of the wall. Cover it with fiberglass drywall for a fire barrier and then move the wall into place. Level it and tie it into the framing.

If you leave it a few inches from the foundation wall, you'll never have to worry about moisture.